I have a bushmaster xm15-e2s, with what appears to be a m16a1 upper receiever. Should I shoot .223 rounds or 5.56? it says on the side of the rifle, Cal 223-5.56mm. So I am guessing I could shoot either one? I bought some cheap Brown Bear ammo, which is .223 rem. Its been about 3 years since I have shot an assualt rifle, in the Marine Corps, my first that on the rounds I bought were that they appeared to be much smaller than the ones shot in the military, I dunno maybe I just forgot.

Quoted: I have a bushmaster xm15-e2s, with what appears to be a m16a1 upper receiever. Should I shoot .223 rounds or 5.56? it says on the side of the rifle, Cal 223-5.56mm. So I am guessing I could shoot either one? I bought some cheap Brown Bear ammo, which is .223 rem. Its been about 3 years since I have shot an assualt rifle, in the Marine Corps, my first that on the rounds I bought were that they appeared to be much smaller than the ones shot in the military, I dunno maybe I just forgot.

Shoot either .223 or 5.56.  I shoot anything in mine from Wolf to xm193

it's chambered for 5.56, the markings on the receiver don't really mean anything it's what is stamped on the barrel that matters.  You can shoot either 5.56 or .223 in a 5.56.  It must be you just forget what the rounds look like because 5.56 and .223 are externaly the same.

height=8

Quoted: height=8 Quoted: What do I shoot in my AR?     Bullets.   The pointy end goes towards the bad guy.  Next question?